Myxococcus xanthus undergoes starvation-induced, multicellular development, a process culminating in the formation of spore-filled fruiting bodies. Development requires a solid surface, a high density of starving cells, and cell-cell signaling to coordinate the program. Fruiting body development provides an excellent model system for studies of multicellular development and cell-cell signaling, largely because of its simplicity and the variety of genetic tools at hand. The goal of the proposed research is to elucidate the mechanism of cell-cell signaling used by M. xanthus to coordinate an early stage of its multicellular development. It has been shown that certain amino acids and peptides are the extracellular A-signal (also called A-factor) required early in development of M. xanthus. Mutants (asgA, asgB, and asgC) that fail to release A-signal have been identified, and the asgA and asgB gene have been cloned. The first aim of this project is to determine the functions of the asgA and asgB genes and the roles that their gene products play in the extracellular release of A- signal. Intergenic suppressors of asgA and asgB gene will be determined, and data bases will be searched for similarities with other genes. A null phenotypes of the genes will be characterized, and lacZ fusion genes will be constructed to study the regulation of the asg genes during growth and development. Although the genes (asg) required for A-signal release have been identified, the genetic components involved in A-signal receptor(s) and other components of the A-signal-response system. Mutants that can no longer express an A-signal-dependent, lacZ fusion gene in response to extracellular A-signal will be isolated using a blue/tan color screen. Toxic amino acid and peptide analogs will be used to select for resistant mutants that are defective in amino acid and peptide transport; these resistant mutants will aid in determining whether signal uptake is required to elicit the response. The possibility that putative A-signal receptors/transducers can functionally replace E. coli proteins that mediate the chemotactic response to amino acids will be explored.